1. Field of the Invention
The present invention relates to a secondary molding apparatus for forming a final product by melting and deforming a top portion of each of protrusions of a primary molded product having a plurality of the protrusions erected on a surface of a flat base material made of thermoplastic synthetic resin.
2. Description of the Related Art
According to Published Japanese Translations of PCT International Publication No. 8-508910, Japanese Patent Application Laid-Open No. 9-322811 and No. 9-322812, a primary product having a plurality of protrusions erected integrally on the surface of a flat base material is continuously molded of thermoplastic synthetic resin and then the base material is transferred through a transfer path. Meanwhile, the base material is supported from below in a secondary molding area provided halfway of the transfer path, and a top portion of each of the protrusions is heated and pressed by a heating/pressing unit such as a heating roller, a heating plate or the like so that it is deformed. As a result, for example,. male members of a surface fastener are molded.
According to the aforementioned Publication No. 8-508910, molten resin is supplied from an extruder or the like to the surface of a rotating cylinder having a plurality of blind holes formed in a circumferential face along an axis and in the circumferential direction such that they are directed linearly toward the axis. Part of the molten resin is pressed into the blind holes so as to mold each protrusion. At the same time, flat base material is molded with the molten resin continuously on the surface of the cylinder integrally with proximal ends of the protrusions. This continuously molded product is supported by a surface of the rotating cylinder and cooled while it is rotated. Then, after being separated from the cylinder, the male surface fastener primary product is obtained. This male surface fastener primary product is transferred to the secondary molding area, in which a circular engaging head portion whose top surface is dented is molded on a tip end of each protrusion erected on the surface of the base material so that the male surface fastener as a final. product is produced.
On the other hand, as disclosed in the aforementioned Japanese Patent Application Laid-Open No. 9-322811 and No. 9-322812, a plurality of V-shaped or Y-shaped blind holes are formed in the circumferential surface of the rotating cylinder like the above described example. The primary molded product of the male surface fastener is molded by a rotation of the cylinder as described above, and after that, the tip end of the V-shaped or Y-shaped protrusion erected on the surface of the base material is heated and pressed in the secondary molding area so that it is deformed. As a result, the engaging head portion having a peculiar shape in which the tip portion of each of the protrusions erected from the surface of the base material is deformed to substantially inverse L shape or substantially T shape, and expanding portions expanding horizontally to the right and left on the tip portion is molded so as to produce the male surface fastenet as the final product.
According to production methods for the male surface fasteners disclosed in the patent publications, because an engaging element each having a peculiar engaging head portion is molded, although an engaging force thereof is lower than that of a conventional mushroom-shaped engaging element, minute engaging elements can be molded in a high density since the protrusion of the primary molded product has a simple configuration. For example, this is effective for an engaging/disengaging device of a disposable diaper. Particularly, in the engaging element formed in a substantially inverse L shape or substantially T shape, having an engaging head portion with horizontally expanding portions molded at a tip thereof, the engaging head portion itself has a higher stiffness than the other portions of the engaging element. Therefore, a necessary engaging force and some extent of separation resistance are secured with the existence of the expanding portions.
On the other hand, deformation of the aforementioned protrusion of the primary molded product which comes into contact with a heating member such as a heating roller and a heating plate disposed on the pressing side of the heating/pressing unit installed in the secondary molding area is determined depending on the heating temperature and contact time of the heating member. When it is intended to press and deform the engaging element to desired shape, the pressing force needs to be controlled to be optimum as well as the heating time and contact time. Further, in order to make the secondary molding speed adapt to the primary molding speed, the secondary molding speed has to be high. For this purpose, a desired thermal capacity and heating source have to be secured. As a result, multi-purpose control system is needed so that inevitably the apparatus is enlarged thereby a large installation space being required.
The present invention has been accomplished to solve the above problems, and therefore, an object of the present invention is to provide a secondary molding apparatus for molding protrusions of synthetic resin erected on the surface of a flat base material, which can be installed in a small installation space and in which the secondary molding speed can be changed arbitrarily and no useless heat history is given to other portions than a portion to be deformed upon deformation.
The above object of the invention can be achieved as described below.
There is provided in this invention a secondary molding apparatus for molding a top portion of each of a plurality of protrusions of a primary molded product having the protrusions integrally erected on the surface of a flat base material to a desired shape by melting and deforming the top portion thereof, the secondary molding apparatus for molding the protrusions of synthetic resin erected on the surface of the flat base material, comprising: a transfer path for the primary molded product; and a pressing member and an internal heating unit disposed vertically at a predetermined interval across the transfer path, wherein the pressing member is disposed at a position in which it presses and deforms the top portion of the protrusion and the internal heating unit is disposed at a position in which it comes into contact with a rear surface of the flat base material.
The primary molded product having a plurality of the protrusions erected on the surface of the flat base material molded by the primary molding apparatus is supplied continuously through the transfer path to the secondary molding apparatus. In the primary molded product supplied to the secondary molding apparatus, the rear surface of the flat base material is supported by the internal heating unit and the top end of the protrusion erected on the surface of the flat base material is pressed by the pressing member. The internal heating unit mentioned here means a unit for heating the synthetic resin molded product by itself as a heat generating body. This internal heating unit intensively heats the top end of the protrusion pressed by the pressing member. Therefore, thermal capacity is concentrated on only the molten and deformed portion, so that molding is enabled without giving unnecessary heat history to other portions. Further, because the internal heating unit is capable of controlling a local heating speed easily and allows quick heating/cooling, molding temperature and molding speed can be controlled arbitrarily. Therefore, the secondary molding suitable for a molding speed of the primary molded product can be achieved.
Preferably, use of the ultrasonic oscillator or high frequency oscillator is provided as the internal heating unit. Because these internal heating units are capable of securing a desired heating speed and temperature without enlarging the size of the internal heating unit, the installation space can be reduced, a desired molding speed can be obtained and the above described function effect can be exhibited sufficiently.
Further preferably, the pressing member is provided, and still preferably, a rotating roller supported by a shaft disposed perpendicular to a direction of crossing the transfer path is employed as the pressing member. Further preferably, a sheet material including an area in which a gap relative to the transfer path decreases gradually is employed. Because the heating area for-the secondary molded product heated by the internal heating unit is concentrated on the pressing area pressed by the pressing member, the heating speed may be increased quickly, thereby the molding speed is increased. As a result, regardless of whether the rotating roller or the sheet material is used, the size of the secondary molding apparatus is reduced effectively as compared to the conventional one.